172991309 has 2 divisors, whose sum is σ = 172991310. Its totient is φ = 172991308.

The previous prime is 172991267. The next prime is 172991323. The reversal of 172991309 is 903199271.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 117115684 + 55875625 = 10822^2 + 7475^2 .

It is a cyclic number.

It is not a de Polignac number, because 172991309 - 2⁸ = 172991053 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (172991369) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 86495654 + 86495655.

It is an arithmetic number, because the mean of its divisors is an integer number (86495655).

Almost surely, 2^172991309 is an apocalyptic number.

It is an amenable number.

172991309 is a deficient number, since it is larger than the sum of its proper divisors (1).

172991309 is an equidigital number, since it uses as much as digits as its factorization.

172991309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 30618, while the sum is 41.

The square root of 172991309 is about 13152.6160515694. The cubic root of 172991309 is about 557.1961346221.

The spelling of 172991309 in words is "one hundred seventy-two million, nine hundred ninety-one thousand, three hundred nine".